Method of signaling particular types of resource elements in a wireless communication system

ABSTRACT

A method of signaling particular types of resource elements in a wireless communication system is disclosed. The method can include, at a wireless terminal, receiving ( 610 ) a message providing information of a set of allocated resource elements carrying data intended for the wireless terminal. The method can include receiving ( 620 ) an indication corresponding to a resource element of a particular type within the set of allocated resource elements. The method can include decoding ( 630 ) resource elements that carry data intended for the wireless terminal based on the message providing information and based on the indication.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to wireless communications andmore particularly to signaling data mapping in an orthogonal frequencydivision multiplexed (OFDM) wireless communication system.

BACKGROUND

In wireless OFDM communication systems, a single OFDM symbol is composedof multiple subcarriers in frequency. Data modulation symbols aredirectly mapped onto these subcarriers. Some of the subcarriers may bereserved for reference/pilot symbols to assist demodulation at the UserEquipment (UE). Further, all available subcarriers may be sub-dividedinto sets or groups of subcarriers for allocation to users with reducedoverhead of signaling.

In typical OFDM based systems like 3^(rd) Generation Partnership Project(3GPP) Long Term Evolution (LTE), a block of 14 consecutive OFDM symbolsare referred to as a subframe. Each sub-carrier location in each of theOFDM symbols is referred to as a resource element (RE), since a singledata modulation symbol can be mapped to such a resource element. Aresource block (RB) is defined as a block of REs composing of a set of12 consecutive sub-carrier locations in frequency and 7 symbols of aslot. Each subframe is made of two slots, and hence 14 symbols. Aminimum resource unit allocated to a user is the two RBs correspondingto two slots in a subframe for a total of 2×12×7 REs.

Some of the REs in the RB maybe reserved for Control Channel functions,the locations of which is known to the UE. The disclosure morespecifically pertains to the data carrying portion of the RB. This is,for example, referred to as Physical Data Shared Channel (PDSCH) inRelease-8 LTE. REs in the rest of the document refer to REs in such datacarrying portion of the RBs.

Some of the REs in a RB are reserved for reference symbols (RSs) (alsoreferred to as pilots) to help in the demodulation and othermeasurements at the UE. These reference symbols, as defined in Release 8LTE can be further divided into two types. The first type iscell-specific reference symbols (CRS), which are cell-specific and“common” to all users, and are transmitted in all the RBs. CRS may ormay not correspond to actual physical antennas of the transmitter, butCRS are associated with one or more antenna “ports”, either physical orvirtual.

The second type is user-specific or dedicated reference symbols (DRS),which are user-specific and hence applicable to that user only, andallocated in the RB's allocated to that user. Furthermore, DRS typicallycorrespond to “precoded” or beam-formed RS, which can be directly usedby a user for the demodulation of the data streams.

The location of the reference symbols is known to the user equipmentfrom higher layer configurations. For example, depending on the numberof antenna ports as configured by a transmission unit, a user equipmentknows the location of all the reference symbols corresponding to allconfigured antenna ports. As another example, when a user equipment isinstructed to use DRS, the user also knows the DRS locations which maydepend on the user identification.

The data symbols intended for a user in his allocated RBs are mapped tothe remaining set of REs after provisioning for the reference symbols.There is no ambiguity on data mapping between the user equipment and thetransmission unit once the RS locations are clear.

In a future migration of a system, user-specific RS may be used widelywith advanced Multiple-Input Multiple-Output (MIMO) modes likeCoordinated Multipoint transmission (COMP) and multi-user (MU) MIMOmodes. Multiuser MIMO schemes refer to MIMO schemes where data istransmitted simultaneously to more than one user from the same set ofRBs. A coordinated multipoint scheme is a scheme where data istransmitted to one or more users by coordinated scheduling and/or jointtransmission from one or more transmission points. It is clear in such acase, that a user allocation may have to support reference symbols thatmay correspond to other users and/or other transmission points.

On the other hand, the advantage of using DRS for demodulation at theuser equipment has two primary advantages. The actual transmission modedetails, such as number of users, number and identity of transmissionpoints, etc, need not be signaled to a user, as long as he canreconstruct the channel based on the DRS. Further, this allows moredynamic changes to the transmission mode(s) without the need tosemi-static configuration by the higher layers, since a user need not bemade aware of such configurations explicitly.

However, due to obligation of the assisting transmission points in aCoMP transmission or provisioning reference symbols for other users in aMU transmission, additional reference symbols may have to be supported.There is a need for a method of signaling a particular type of resourceelement in a wireless communication system.

The various aspects, features and advantages of the invention willbecome more fully apparent to those having ordinary skill in the artupon a careful consideration of the following Detailed Descriptionthereof with the accompanying drawings described below. The drawings mayhave been simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary illustration of a wireless communication systemaccording to a possible embodiment;

FIG. 2 is an exemplary schematic block diagram of a wirelesscommunication unit according to a possible embodiment;

FIG. 3 is an exemplary illustration of resource allocation to differentusers in an OFDM communication system according to a possibleembodiment;

FIG. 4 is an illustration of a resource block (RB) as in Release-8specification of LTE with Common RS (CRS) and Dedicated RS (DRS);

FIG. 5 is an illustration of a resource block (RB) as in Release-8specification of LTE with reference symbols and REs of a particulartype;

FIG. 6 is a flowchart of an embodiment of operation at the UserEquipment (UE);

FIG. 7 is a flowchart of an embodiment of operation at the Base unit;

FIG. 8 is an embodiment illustration of Coordinate Multipoint (COMP)operation with the reference symbol REs and an example of REs of aparticular type; and

FIG. 9 is an embodiment illustration of Multiuser (MU) operation withthe reference symbol REs and an example of REs of a particular type.

DETAILED DESCRIPTION

Embodiments provide for method of signaling particular types of resourceelements in a wireless communication system. The method can include, ata wireless terminal, receiving a message providing information of a setof allocated resource elements carrying data intended for the wirelessterminal. The method can include receiving an indication correspondingto a resource element of a particular type within the set of allocatedresource elements. The method can include decoding resource elementsthat carry data intended for the wireless terminal based on the messageproviding information and based on the indication.

Embodiments provide for method of signaling particular types of resourceelements in a wireless communication system. The method can signal dataresource element mapping. The method can include transmitting a messageproviding information of a set of allocated resource elements carryingdata intended for a wireless terminal. The method can includetransmitting an indication in an orthogonal frequency divisionmultiplexing system, the indication corresponding to a resource elementof a particular type within the set of allocated resource elements. Themethod can include mapping data modulation symbols to the set ofallocated resource elements based on the indication.

Embodiments provide for a wireless terminal. The wireless terminal caninclude a transceiver configured to receive a message providinginformation of a set of allocated resource elements carrying dataintended for the wireless terminal and configured to receive anindication corresponding to a resource element of a particular typewithin the set of allocated resource elements. The wireless terminal caninclude a processor coupled to the transceiver, the processor configuredto control operations of the wireless terminal, the processor configuredto decode resource elements that carry data intended for the wirelessterminal based on the message providing information and based on theindication.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth herein.

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

The present invention comprises a variety of embodiments, such as amethod, an apparatus, and an electronic device, and other embodimentsthat relate to the basic concepts of the invention. The electronicdevice may be any manner of computer, mobile device, or wirelesscommunication device.

In FIG. 1, a wireless communication system 100 can include one or morefixed base infrastructure units 101, 102 forming a network distributedover a geographical region for serving remote units. A base unit 101 mayalso be referred to as an access point, access terminal, base, basestation, Node-B, eNode-B, Home Node-B, Home eNode-B, relay node, or byother terminology used in the art. The one or more base units 101, 102can each comprise one or more transmitters for downlink transmissionsand one or more receivers for receiving uplink transmissions. The baseunits 101, 102 are generally part of a radio access network thatincludes one or more controllers communicably coupled to one or morecorresponding base units. The access network is generally communicablycoupled to one or more core networks, which may be coupled to othernetworks, like the Internet and public switched telephone networks,among other networks. These and other elements of access and corenetworks are not illustrated but are well known generally by thosehaving ordinary skill in the art.

In FIG. 1, the one or more base units can serve a number of remote units103, 104, 105, 106, 107 within a corresponding serving area, forexample, a cell or a cell sector, via a wireless communication link. Theremote units 103, 104, 105, 106, 107 may be fixed or mobile. The remoteunits 103, 104, 105, 106, 107 may also be referred to as subscriberunits, mobiles, mobile stations, users, terminals, subscriber stations,user equipment (UE), user terminals, wireless communication devices, orby other terminology used in the art. The remote units 103, 104, 105,106, 107 can include one or more transmitters and one or more receivers.In FIG. 1, the base unit 101 can transmit downlink communication signalsto serve remote units 103, 105, 107 in the time and/or frequency and/orspatial domain. The remote units 103, 105, 107 can communicate with baseunit 101 via uplink communication signals. A remote unit 104, 106 cancommunicate with base unit 102 and/or base unit 101. Sometimes the baseunit 101 is referred to as a serving, or connected, or anchor cell forthe remote units 103, 105, 107 and correspondingly base unit 102 isreferred as an anchor cell for remote units 104, 106. The remote units103, 104, 105, 106, 107 may have half duplex (HD) or full duplex (FD)transceivers. Half-duplex transceivers do not transmit and receivesimultaneously whereas full duplex terminals do. The remote units maycommunicate with the base units via a relay node. Conventionally, asingle point operation is when an anchor base unit (for example, 101)transmits data to remote units (for example, 103, 105, 107 here) servedby it. In a multiuser scheme, such a base unit 101 may transmit datasimultaneously over the air and on the same set of REs/RBs to two ormore users 103, 105, 107. In Coordinated Multipoint MIMO (COMP)operation, two or more neighboring base units 101, 102 may transmitsimultaneously to one or more units 103, 104, 105, 106, 107 bycoordinating data to be transmitted to the individual users and takeinto account interference channel related information. In such a case, aremote unit exchanges control information with its anchor base unit, butmay receive transmissions from other base units. It may be partly orfully unaware (or blind to) of the exact details/parameters of suchcoordinated transmission.

In one implementation, the wireless communication system can becompliant with the 3^(rd) Generation Partnership Project (3GPP)Universal Mobile Telecommunications System (UMTS) Long Term Evolution(LTE) protocol, also referred to as Evolved Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (EUTRA) orRelease-8 (Rel-8) 3GPP LTE or some later generation thereof (forexample, Release-10 or LTE-Advanced), wherein the base unit 101 cantransmit using an orthogonal frequency division multiplexing (OFDM)modulation scheme on the downlink and user terminals 103, 104 cantransmit on the uplink using a single carrier frequency divisionmultiple access (SC-FDMA) scheme. More generally, however, the wirelesscommunication system 100 may implement some other open or proprietarycommunication protocol, for example, WiMAX, among other protocols.

In FIG. 2, a wireless communication unit or terminal 200 can include acontroller/processor 210 communicably coupled to a memory 212, adatabase interface 214, a transceiver 216, and an input/output (I/O)device interface 218 connected through a system bus 220. The wirelesscommunication unit 200 may be implemented as a base unit or a remoteunit and can be compliant with the protocol of the wirelesscommunication system within which it operates, such as, for example, the3GPP LTE Rel-8 or later generation protocol discussed above. In FIG. 2,the controller/processor 210 may be implemented as any programmedprocessor. However, the functionality described herein may also beimplemented on a general-purpose or a special purpose computer, aprogrammed microprocessor or microcontroller, peripheral integratedcircuit elements, an application-specific integrated circuit or otherintegrated circuits, hardware/electronic logic circuits, such as adiscrete element circuit, a programmable logic device, such as aprogrammable logic array, field programmable gate-array, or the like. InFIG. 2, the memory 212 may include volatile and nonvolatile datastorage, including one or more electrical, magnetic or optical memoriessuch as a random access memory (RAM), cache, hard drive, read-onlymemory (ROM), firmware, or other memory device. The memory 212 may havea cache to speed access to specific data. Data may be stored in thememory 212 or in a separate database. The database interface 214 may beused by the controller/processor 210 to access the database. Thetransceiver 216 can be capable of communicating with user terminals andbase stations pursuant to the wireless communication protocolimplemented. In some implementations, for example, where the wirelesscommunication unit 200 is implemented as a user terminal 103, thewireless communication unit 200 can include an I/O device interface 218that connects to one or more input devices that may include a keyboard,mouse, pen or finger-operated touch screen or monitor, voice-recognitiondevice, or any other device that accepts input. The I/O device interface218 may also connect to one or more output devices, such as a monitor,printer, disk drive, speakers, or any other device provided to outputdata.

In operation, the transceiver 216 can receive a message providinginformation of a set of allocated resource elements carrying dataintended for the wireless terminal 200. The transceiver 216 can receivean indication corresponding to a resource element of a particular typewithin the set of allocated resource elements. The processor 210 cancontrol operations of the wireless terminal 200. The processor 210 candecode resource elements that carry data intended for the wirelessterminal 200 based on the message providing information and based on theindication.

Referring back to FIG. 1, the network base station 101 may have a set ofphysical antennas 108 for making a data transmission to the UE devices103, 105, 107. A network base station 101 may coordinate with one ormore other network base stations 102 to make the data transmission. Adata transmission may be the act of sending data, regardless of the typeof data or the form of the transmission. A data transmission mayencompass one or more data streams via one or more effective channels.An antenna port may be associated with an actual or effective channelobservable to a UE device 103. One physical antenna 108 may map directlyto a single antenna port, in which an antenna port corresponds to anactual physical antenna. Alternately, a set or subset of physicalantennas 108, or antenna set 108, may be mapped to one or more antennaports after applying complex weights, a cyclic delay, or both to thesignal on each physical antenna 108. The physical antenna set 108 mayhave antennas from a single base station 101 or from multiple basestations. The weights may be fixed as in an antenna virtualizationscheme, such as cyclic delay diversity (CDD). The associated pilots maybe different or common to all UE devices 103, 104, 105, 106, 107. Theprocedure used to derive antenna ports from physical antennas 108 may bespecific to a base station 101 implementation and transparent to the UEdevices 103, 104, 105, 106, 107.

In an orthogonal frequency division multiplexing (OFDM) system, theentire bandwidth can be divided into orthogonal subcarriers. A frequencysubcarrier over a period of one OFDM symbol can be referred to as aresource element (RE). A set of OFDM symbols forms a subframe withinwhich the base station 101 can allocate a set of REs in time and/orfrequency domain to each UE for data transmission. An example of asubframe in an OFDM system is shown in FIG. 3 where UE 103, 105, and 107are each allocated with a set of REs in that subframe. These allocationsmay or may not be adjacent in the frequency domain. There may or may notbe a definition of Resource Block (RB) which is a set of contiguous (oreven non-contiguous) subcarriers in frequency domain over a duration ofseveral OFDM symbols. If RB is defined as a base unit of allocation,which is assumed in FIG. 3, resource allocation can be in multiples ofRBs. Note that RE allocation to each UE can consist of multiple RBs thatmay or may not be adjacent to each other. In FIG. 3, allocation to UE103 comprises of 2 non-adjacent RBs (i.e., RB 306 and RB 310).

A UE typically receives a control message that provides information of aset of allocated REs carrying data symbols intended for the UE. Such anallocation may be represented as a number of RBs, along with theirlocations. It is generally understood to each UE that within theallocation, typically there are non data-carrying REs that are used aspilots or reference symbols (RS) whose locations are known to the UE. RSare provided for UEs to estimate the channel for the purpose of datademodulation or some kind of measurement as required to be reported backto the base station. As described before, there may be two types of RS:cell-specific RS or CRS that are intended for use by all UEs in thatcell and dedicated (i.e., user-specific) RS or DRS that are intended foruse by the particular UE only

In the example of frame structure shown in FIG. 3, a base station 101may send reference symbols in both time and frequency domains to enableUE 103, 105, and 107 to obtain channel knowledge in both domains fordemodulation. The set of CRS 302 may be scattered across the entiresystem bandwidth to allow UE 103, 105, and 107 to estimate the channelfor the whole band. The set of CRS 302 may be scattered across the time,or frame, so that all UE served by the same base station may track thetime variation of the channel. CRS are sent regardless of the number ofUEs and their allocation.

In FIG. 3, DRS 304 may also be sent to enable a particular UE 103 toobtain an effective channel that is only useful for that UE's datademodulation. Typically, the base station 101 may embed DRS 304 in theuser-specific allocation resource regions. It needs to be pointed outthat even though both types of RS are shown in FIG. 3, they may or maynot be present simultaneously. For example, there may be only DRS oronly CRS present in the system. From each UE's perspective, DRS may ormay not be present. For example, UE 103 is allocated with DRS in itsallocated RBs 306 and 310, while UE 105 is not allocated with any DRS.

More details are provided in the following on the function of CRS andDRS in an OFDM transmission, where the transmitter has multiple antennasand the receiver has at least one and typically more than one antenna.Common reference symbols or cell-specific reference symbols (CRS) may besent from the base station 101 intended for all UE devices in the cellas mentioned before. The CRS pattern (i.e., RS locations and theirvalues) may differ from cell to cell, thus the term “cell-specific,” butthey can be used by all UEs in the cell, thus the term “common.” A UEdevice typically learns about the CRS pattern after it acquires theknowledge of a cell ID. For example, in 3GPP LTE, CRS have a uniformspacing with a starting location in frequency domain having an offsetthat depends on the Cell ID. There are three possible offset valueswherein the offset is relative to the first RE in an RB.

In the case of multiple transmit antennas, the CRS may often be dividedinto a number of subsets, each subset corresponding to a physicalantenna port or a “virtual” antenna port where the virtualizationprocess may have a group of radiating elements transmitting the samesignal in a fixed manner as explained earlier. In a virtualizationprocess, the signal may be pre-determined based on a base station 101implementation, but otherwise common and transparent to all UE devices.In the example of LTE specification again, CRS may be divided into 1, 2or 4 subsets corresponding to 1, 2 or 4 antenna ports whose number isannounced by the eNB. The actual physical antennas or radiating elementsmay belong to one or more such subsets used for virtualization. Moregenerally, virtualization may be viewed as mapping a set of radiatingelements to a set of common antenna ports, where such virtualization iscommon to all UEs.

As opposed to CRS that are intended for all UEs, dedicated referencesymbol (DRS), or user-specific pilots, may be intended for a particularUE. In a typical operation, a DRS may be embedded within the user'sallocation, such as subcarriers or subbands or RBs as defined in LTE. ADRS may correspond to “precoded” reference symbol, where precoding maybe performed in a similar way to the preceding applied on data symbols.

The “preceding” operation is explained in the following. The basestation transmits a signal via weighting each antenna signal with acomplex value, an operation referred to as preceding, which may bemathematically represented by the matrix equation:Y=HVs+nin which, when transmitting one data stream, or rank-1, may berepresented as:

$\begin{bmatrix}y_{1} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{1,1} & \ldots & h_{1,N_{T}} \\\vdots & \ddots & \vdots \\h_{N_{R},1} & \ldots & h_{N_{R},N_{T}}\end{bmatrix}\begin{bmatrix}v_{1} \\\vdots \\v_{N_{T}}\end{bmatrix}}s} + n}$in which, when transmitting two data streams, or rank-2, may berepresented as:

$\begin{bmatrix}y_{1} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{1,1} & \ldots & h_{1,N_{T}} \\\vdots & \ddots & \vdots \\h_{N_{R},1} & \ldots & h_{N_{R},N_{T}}\end{bmatrix}\begin{bmatrix}v_{1,1} & v_{1,2} \\\vdots & \vdots \\v_{N_{T},1} & v_{N_{T},2}\end{bmatrix}}\begin{bmatrix}s_{1} \\s_{2}\end{bmatrix}} + n}$where y₁ . . . y_(N) _(R) may be the received data at the UE receiveantenna #1 to #N_(R), respectively. In the example with a rank-1transmission, or a transmission with one data stream denoted as “s”, Vmay be a precoding vector with weights v_(1,1) . . . V_(N) _(T) _(,1)for base station transmit antenna #1 to #N_(T) respectively. In anembodiment with a rank-2 transmission, or a transmission with two datastreams s1 and s2 on the same subcarrier, V may be a precoding matrix.Matrix H may be the propagation channel matrix between transmit antennasand receive antennas, with entry h_(ij) representing a channel betweenthe jth transmit and ith receive antennas. Value n may represent noiseand interference. The precoding weights V, either a vector or matrix,may be determined by the base station, typically based on the channelparticular to the UE or can be UE-specific and may also take intoaccount a preference indicated by feedback from the UE. Further thematrix HV can be referred to as the effective channel between a user'sdata streams and its receivers. Effective channel, instead of thepropagation channel H, is all a UE needs for demodulation purpose. Theprecoding weights may or may not be constrained to a predefined codebookthat consists of a set of pre-defined vectors or matrices. In anembodiment with constrained precoding, the precoding matrix may besignaled by the base unit efficiently with a precoding matrix index(PMI), or an index to a precoding matrix within a predefined codebook.The term “matrix” may include the degenerated special case of vector. Inthe most generic sense, the term “preceding” may refer to any possibletransmission scheme that may be deemed as mapping a set of data streamsto an antenna set using a matrix V. The term “preceding” may include an“open-loop” transmission as a special “preceding” with unweightedantennas and any antenna virtualization schemes, such as cyclic delaydiversity (CDD).

The applied precoding could be based on corresponding feedback from theUE or channel measurements at a base station. In a simple single-usersingle base unit scheme, one set of DRS could be defined correspondingto the effective precoded channel (i.e., “HV” in the above equation). Iftwo streams are transmitted to a user in a rank-2 transmission, thenonly 2 DRS ports (i.e., 2 subsets of DRS each corresponding to aprecoded antenna port) are sufficient, even though the actual signaltransmission may come from all the N_(T) antennas at the base unit whereN_(T) can be greater than 2.

In another method, an effective channel may also be constructed based onCRS which carry the information of propagation channel and theuser-specific precoding matrix signaled to a UE.

As it can be seen that one of the difference between DRS and CRS is thatthe presence of DRS is often known and of interest to a particular UE.FIG. 4 illustrates, in a block diagram, one embodiment of how DRS andCRS may be embedded in a RB. Note that there may or may not be adefinition of RB in a frame when REs are assigned to a set of UEs. TheRB 400 shown in FIG. 4 can correspond to RB 306 in FIG. 3. Inparticular, the example RB shown in FIG. 4 is an RB as defined in theLTE specification. RB in LTE spans 12 subcarriers in frequency and spansa slot in time, where two slots form a “subframe”, and each slot iscomposed of 7 OFDM symbols in time. CRS shown in an RB 400 may bedivided into several subsets with each being associated with a differentantenna port. For example, a RB 400 may have a first CRS subset 404associated with an antenna port #0 and a second CRS subset 406associated with an antenna port #1, respectively with each subset havingfour locations in an RB 400. Further, the RB 400 may have a third CRSsubset 408 associated with an antenna port #2 and a fourth CRS subset410 associated with an antenna port #3. In addition to any CRStransmitted from the base station 101, additional DRS may also betransmitted within the UE-specific allocation. The RB 400 may have a setof DRS 412, in this example six DRS 412, associated with a “precoded”antenna port #5. In this case, the antenna port #5, rather than being anactual antenna, may correspond to the effective channel seen at the UEdevice 103 after the base station 101 applies precoding on a set ofphysical antennas 108. The precoding may take the form of beamforming,where a vector of weights may be applied to an antenna set to obtain aneffective channel.

DRS pattern (i.e., DRS locations and the associated reference symbolvalues) is known to the UE as a predetermined function of someparameters such as cell ID and user ID.

In a traditional operation, once the UE knows all the RS locations asdescribed above, the UE knows the data-carrying REs within itsallocation. The UE will demodulate these data-carrying REs and decodethe information intended for itself. However, there may be a need for abase station to further designate a set of particular type of RE withinthe set of allocated REs for special usage. For the sake of conveniencein later description, we also refer to RE of a particular type as“special RE” sometimes. An example of REs of a particular type within anRB is shown in FIG. 5. Compared with FIG. 4, special REs 520, 521, 522,and 523 are shown. Note that number of special REs and their locationshown in FIG. 5 are just example for illustration purposes. Of course,the presence of special REs is independent from the presence and patternof CRS, or DRS, or both as shown in FIG. 4 and FIG. 5. The UE, afterreceiving such indication corresponding to a RE of a particular type,can treat these special RE differently from normal data-carrying RE inthe process of data demodulation and decoding.

Before discussing the usage of these REs of a particular type, it isnoted that such indication corresponding to the RE of the particulartype may be just a bit-field within the control message received fromthe base station that provides information of the set of allocated REsin a normal operation. Such indication may include the indication of thepresence or absence of any such RE of a particular type. If thesespecial REs are indeed present, the indication may include the locationsof at least one RE of a particular type, as well as possibly theinformation about the nature of the special REs so that a UE knows howto treat them.

There are many ways to convey the location information of special REs.In one example, the information is conveyed as an index to a set ofpredefined and allowable patterns. In another example, the locationinformation of the special REs is indicated by a value representing arelationship to a known reference pattern. For instance, the referencepattern can be cyclic shifted (i.e. offset) in frequency or time domainto get the special RE locations. The known reference pattern maycorrespond to any RS pattern as long as it is known to the UE. It can bea cell-specific RS pattern of a serving or a neighboring cell known tothe UE, or a user-specific RS pattern known to the UE.

FIG. 6 is an exemplary flowchart outlining the operation of a methodaccording to one embodiment. At 610, a message is received that providesinformation of a set of allocated resource elements carrying dataintended for a wireless terminal. At 620, an indication is received thatcorresponds to a resource element of a particular type within the set ofallocated resource elements. At 630, resource elements that carry dataintended for the wireless terminal are decoded based on the messageproviding information and based on the indication.

FIG. 7 is an exemplary flowchart outlining the operation of a methodaccording to one embodiment. At 710, a set of resource blocks areallocated to a user and a message providing information of the set ofallocated resource elements carrying data intended for a wirelessterminal is transmitted to the wireless terminal. At 720, the set ofresource elements of a particular type are determined for a desiredtransmission mode, such as multi-unit or coordinated multipoint. At 730,an indication is transmitted that corresponds to a resource element of aparticular type within the set of allocated resource elements. At 740, asub frame is encoded by mapping data modulation symbols to resourceelements in the sub frame based on the indication.

The use case of REs of a particular type is discussed in the followingembodiments.

In one embodiment, the RE of a particular type is an RE that does notcontain any information data symbol intended for the UE. Therefore, theUE should ignore those special REs during data demodulation anddecoding.

This scenario arises when two or more cells serve the same UE in acoordinated transmission (i.e., CoMP as mentioned earlier). Consider theexample of coordinated transmission between two base stations 801, 802to a single UE 808 as illustrated in FIG. 8. Both base stations 801, 802jointly transmit same data to the UE 808, which is nominally served by,say, its serving cell base station 801. In this example, the basestation 802 is the coordinating (or “assisting”) base station from theperspective of UE 808. This advanced CoMP operation can require that thebase stations 801, 802 have the same data content intended for UE 808.But UE 808 may not be aware of the actual transmission points and hence,from its perspective, it just assumes normal transmission from basestation 801. As described earlier, the use of DRS can make suchoperation possible as long as the DRS are sent in the same way asdata-carrying REs. UE 808 knows the DRS pattern if base station 801 alsouses them in the case of no coordination. UE 808 may well assume thesame DRS pattern even with coordination, especially since thecoordination is blind to the UE.

Meanwhile, the coordinating base station 802 may often still need totransmit CRS as needed by UEs that deem base station 802 as the servingcells, with or without any coordinated transmission. As mentionedbefore, the CRS pattern for each cell can be different depending on cellID. In the example as illustrated in FIG. 8, the CRS locations for basestation 802 is an offset or shift in frequency domain from the CRSlocations for base station 801. It can be seen from FIG. 8 that a normaldata-carrying RE for UE 808 may correspond to a CRS location of thecoordinating base station 802, which further means that, at those REs,the base station 802 cannot coordinate the transmission to UE 808 withbase station 801 the same way as at other REs. To avoid performance lossat UE 808, base station 801 and 802 may choose to transmit data only onthe set of REs without such conflict. In this case, base station 801needs to indicate to UE 808 that those normally data-carrying REs arenow REs of a particular type, and further more in this embodiment, thespecial REs does not contain any information data symbol intended for UE808 and thus should be ignored during data demodulation and decoding.

In another embodiment, the indication corresponding to the resourceelement of a particular type corresponds to the indication ofsuperposition of reference and data symbols on at least one resourceelement of the particular type. This can be considered as a modificationof the above embodiment, where the special REs still carry data symbolsintended for UE 808, except for the fact that these RE will be differentthan normal data-carrying REs in the sense that base station 802 cannotcoordinate the transmission due to its CRS transmission obligation.Hence UE 808 receives signal on these special REs the superposition ofinformation data symbols sent form its serving cell 801 and thereference symbols from some other base station (cell 802 in this case,but could even be other base station). The indication of these specialREs serves the purpose of alerting the UE to potentially process them ina different way from other data-carrying REs. For example, the UE mayelect to suppress the interference of the superposed reference symbolbefore further extracting useful information from these special REs.

In the above embodiments, the special REs are introduced due tocoordinated transmission from more than one base station where acoordinating base station is obligated to transmit its own CRS thatcould be at an offset location with respect to CRS of the serving cell.The location of special RE can be easily indicated as a frequency-domainoffset (i.e., shift) value where the offset is with respect to areference pattern, which corresponds to the CRS locations of the servingcell in this case. Of course if the cell ID of coordinating cell 802 isknown to UE 808, the UE can also derive the special RE pattern. However,it may be more efficient to signal the shift value than to signal thecell ID of other cells because typically only a limited shift values arepossible (e.g., 3 corresponding to shift values of 0,1,2 in LTEspecifications). The offset value can be, for example, conveyed as anadditional field to the Downlink Control Information (DCI) format, whichis the control message providing information of dynamic resourceallocation to a UE. Furthermore, signaling the shift, due to the smalloverhead, can enable more dynamic switching between differenttransmission modes that require different configurations of special REs.

The usage of special REs is not limited to above coordinatedtransmission cases. In another embodiment, the indication correspondingto the resource element of a particular type corresponds to theindication of a reference symbol pattern specific to a differentwireless terminal. Special REs can be useful for multi-user transmissionwhere a base station transmits different information data symbols tomore than one UE at the same set of REs. However, each UE may havedifferent RS. So reference symbols for a UE could be signaled to anotherUE as special REs.

FIG. 9 is an exemplary illustration of resource blocks 910, 920, and 930according to the above embodiment for multiuser transmission. In thiscase, if DRS are employed, a different DRS port can be allocated foreach stream and each UE. For example if rank-2 transmission is performedto each of the two UEs for a total of four streams transmitted, thenfour DRS ports may be allocated. They can be allocated by FDM (frequencydivision multiplexing or sharing in frequency) as in 910 (two UEs withone stream each), CDM (Code division multiplexing or sharing in codedomain) as in 920 (two UEs with one stream each) or a combination of FDMand CDM as in 930 (two UEs with two streams each). However, eachindividual UE should to be aware of DRS ports corresponding to itsstreams in each case. In presence of DRS for other UE, additionalinformation of these ports may be useful to the UE.

In one implementation, in 910, data symbols are not mapped to any of theDRS REs. In this case from any UE's perspective, the DRS for the otherUE(s) are indicated as special REs that do not contain data informationsymbols intended for this UE. Again, the information of special RElocations may be conveyed as a shift or offset relative to the referenceDRS location known to that UE.

In a modification of the above implementation, data is still transmittedon special REs, superposed with DRS for other users. Specifically, inthe locations of DRS port 0 for UE 0 illustrated in 910, data for UE1may be mapped. This does not result in significant performancedegradation, if the users are spatially separated and the post-precodedsignal power of each user is small as observed by other user. This ispossible, for example, by improved feedback/channel state information atthe base units, which enables them to choose good user pairs with suchseparation and good selection of precoding matrices. In such cases, itis further possible that the DRS signals are boosted by a fixed factorwith respect to the data for improving channel estimation. A UE can takeadvantage of the knowledge of location of the RS ports of the other UEsin MU transmission (signaled as special REs), to modify its interferencecalculations for decoding. More specifically, the knowledge ofsuperposition of other user's DRS on its data coupled with the boostingfactor may be used to modify interference/noise variance estimates atthese locations. In addition to the special RE locations, with theadditional knowledge of other user's pilot sequence (usually dependingon the CellID and a user identifier), a UE can estimate channel ofanother UE for interference cancellation.

In one embodiment, the REs of a particular type are REs on which thereis an absence of any signal transmission from one or more cells. Theprovisioning of such special RE is to allow the UE to “sniff” theinterference characteristic.

The concept of indicating REs of a particular type can be generallyapplied to many other scenarios where there is a need to have the UE tobe aware of the special REs. For example, it can be used to insertadditional RS. A UE that has the capability to at least ignore thespecial REs can mitigate any potential impact due to future evolution ofthe standards when special REs need to be carved out for specialpurposes.

In an example, CRS corresponding to up to 4 antennas are defined inrelease 8 of LTE specification. When more than 4 antennas are supportedin a future version of the LTE specification, some type of RS for eachantenna may be required to allow UE to measure the full spatialcharacteristic of the channels. They can then be referred to as CSI-RS(as in Channel State Information), or CQI-RS (Channel QualityInformation), or LCRS (Low Density CRS). For these measurements, asopposed to demodulation, RS can be transmitted less frequently in time.Nevertheless, when the insertion of new CSI-RS corresponding todifferent or additional antennas can be performed by converting somenormal data-carrying REs to special REs, it is still good to signalthose REs to avoid any performance impact on UE demodulation.

In a future version of the specification (LTE-A/Release 10), CRS portsare not necessarily mandated in every RB. Further, dedicated LTE-Asubframes may also be allocated in systems supporting Release-8 UEs,which do not have to support CRS. In such a case, up to 8 DRS ports maybe defined to support as many as 8 data streams with eight transmitantennas. These may be all be targeted at a single user or to multipleusers. The different patterns possible with different assignments ofnumber of users, number of streams per user and FDM/CDM can beefficiently mapped to set of useful patterns representing locations ofREs of a particular type, e.g., data erasures or increased interferenceor locations to estimate an interfering channel, which can be indexedwith a pre-defined mapping and signaled as a bit pattern in downlinkcontrol signaling.

1. A method of receiving resource allocation at a wireless terminal, themethod comprising: receiving a control message providing information ofa set of allocated resource elements carrying data intended for thewireless terminal; receiving information of a first set of non-zeropower reference signal configuration and a second set of zero powerreference signal configuration, where the first set of non-zero powerreference signal configuration corresponds to one or more referencesymbols corresponding to one or more antenna ports configured forwireless terminal channel measurements, where the second set of zeropower reference signal configuration corresponds to one or more resourceelements where there is no transmission to the wireless terminal, andwhere both the first set of non-zero power reference signalconfiguration and the second set of zero power reference signalconfiguration are from a common set of pre-defined and allowablereference signal configurations; deriving resource elements that carrythe data intended for the wireless terminal excluding the resourceelements associated with the first set of non-zero power referencesignal configuration and the second set of zero power reference signalconfiguration; and decoding resource elements that carry data intendedfor the wireless terminal based on deriving the resource elements thatcarry the data intended for the wireless terminal.
 2. The method ofclaim 1, wherein the set of allocated resource elements corresponds to aset of subcarriers in one or more symbols in an orthogonal frequencydivision multiplexing system.
 3. The method of claim 1, wherein thereference symbol configurations correspond to antenna ports that enablethe measurements of channel state information.
 4. A wireless terminalcomprising: a transceiver configured to receive a control messageproviding information of a set of allocated resource elements carryingdata intended for the wireless terminal and configured to receiveinformation of a first set of non-zero power reference signalconfiguration and a second set of zero power reference signalconfiguration, where the first set of non-zero power reference signalconfiguration corresponds to one or more reference symbols correspondingto one or more antenna ports configured for wireless terminal channelmeasurements, where the second set of zero power reference signalconfiguration corresponds to one or more resource elements where thereis no transmission to the wireless terminal, and where both the firstset of non-zero power reference signal configuration and the second setof zero power reference signal configuration are from a common set ofpre-defined and allowable reference signal configurations; and aprocessor coupled to the transceiver, the processor configured tocontrol operations of the wireless terminal, the processor configured toderive resource elements that carry the data intended for the wirelessterminal excluding the resource elements associated with the first setof non-zero power reference signal configuration and the second set ofzero power reference signal configuration, and the processor configuredto decode resource elements that carry data intended for the wirelessterminal based on deriving the resource elements that carry the dataintended for the wireless terminal.
 5. The wireless terminal of claim 4,wherein the reference symbol configurations correspond to antenna portsthat enable the measurements of channel state information.
 6. A methodof receiving resource allocation at a wireless terminal, the methodcomprising: receiving a control message providing information of a setof allocated resource elements carrying data intended for the wirelessterminal; receiving an indication corresponding to a first set of one ormore resource elements of a particular type within the set of allocatedresource elements, where the one or more resource elements of theparticular type are resource elements that are obtained by shifting aknown reference signal pattern corresponding to a serving cell of thewireless terminal, where the known reference signal pattern comprises asecond set of one or more resource elements; deriving the resourceelements that carry the data intended for the wireless terminalexcluding the resource elements associated with the first set of one ormore resource elements of a particular type and the second set of one ormore resource elements; and decoding the resource elements that carrythe data intended for the wireless terminal based on deriving theresource elements that carry the data intended for the wirelessterminal.
 7. The method of claim 6, wherein the known reference signalpattern corresponds to antenna ports that enable the measurements ofchannel state information on common antenna port reference signals. 8.The method of claim 6, wherein the resource elements of particular typecorrespond to no data transmission to the wireless terminal.
 9. Awireless terminal comprising: a transceiver configured to receive acontrol message providing information of a set of allocated resourceelements carrying data intended for the wireless terminal and configuredto receive an indication corresponding to a first set of one or moreresource elements of a particular type within the set of allocatedresource elements, where the one or more resource elements of theparticular type are resource elements that are obtained by shifting aknown reference signal pattern corresponding to a serving cell of thewireless terminal, where the known reference signal pattern comprises asecond set of one or more resource elements; and a processor coupled tothe transceiver, the processor configured to control operations of thewireless terminal, the processor configured to derive the resourceelements that carry the data intended for the wireless terminalexcluding the resource elements associated with the first set of one ormore resource elements of a particular type and the second set of one ormore resource elements, and the processor configured to decode theresource elements that carry the data intended for the wireless terminalbased on deriving the resource elements that carry the data intended forthe wireless terminal.
 10. The wireless terminal of claim 9, wherein theknown reference signal pattern corresponds to antenna ports that enablethe measurements of channel state information on common antenna portreference signals.
 11. The wireless terminal of claim 9, wherein theresource elements of particular type correspond to no data transmissionto the wireless terminal.
 12. A method of receiving resource allocationat a wireless terminal, the method comprising: receiving a controlmessage providing information of a set of allocated resource elementscarrying data intended for the wireless terminal; receiving anindication corresponding to a first set of one or more resource elementsof a particular type within the set of allocated resource elements,where the one or more resource elements of the particular type areresource elements that are obtained by shifting a known reference signalpattern corresponding to a serving cell of the wireless terminal, wherethe known reference signal pattern comprises a second set of one or moreresource elements; deriving a third set of resource elements excludingresource elements associated with first resource element and secondresource element sets of reference signal configurations; determining afirst nominal interference characteristic on the third set of resourceelements; determining a second interference characteristic on the firstset of one or more resource elements of a particular type; and decodingthe first and third set of resource elements that carry data intendedfor the wireless terminal using the first nominal interferencecharacteristic and the second interference characteristic.
 13. Themethod of claim 12, wherein the indication of corresponding to the firstset of one or more resource elements of a particular type corresponds toan indication of superposition of reference and data symbols on at leastone resource element of the particular type, and wherein the methodfurther comprises suppressing interference on the first of one or moreresource elements to decode the corresponding data symbols using theknowledge of a potential reference symbol transmission on the first setof one or more resource elements from a hypothetical interfering basestation.
 14. A wireless terminal comprising: a transceiver configured toreceive a control message providing information of a set of allocatedresource elements carrying data intended for the wireless terminal andconfigured to receive an indication corresponding to a first set of oneor more resource elements of a particular type within the set ofallocated resource elements, where the one or more resource elements ofthe particular type are resource elements that are obtained by shiftinga known reference signal pattern corresponding to a serving cell of thewireless terminal, where the known reference signal pattern comprises asecond set of one or more resource elements; and a processor coupled tothe transceiver, the processor configured to control operations of thewireless terminal, the processor configured to derive a third set ofresource elements excluding resource elements associated with firstresource element and second resource element sets of reference signalconfigurations, the processor configured to determine a first nominalinterference characteristic on the third set of resource elements, theprocessor configured to determine a second interference characteristicon the first set of resource elements of a particular type, and theprocessor configured to decode the first and third set of resourceelements that carry data intended for the wireless terminal using thefirst nominal interference characteristic and the second interferencecharacteristic.
 15. The wireless terminal of claim 14, wherein theindication corresponding to the first set of one or more resourceelements of a particular type corresponds to an indication ofsuperposition of reference and data symbols on at least one resourceelement of the particular type, and wherein the processor is configuredto suppress interference on the first of one or more resource elementsto decode the corresponding data symbols, using the knowledge of apotential reference symbol transmission on the first set of one or moreresource elements from a hypothetical interfering base station.